296 research outputs found
UVES spectra of young brown dwarfs in Cha I: radial and rotational velocities
Based on high-resolution UVES spectra we found that the radial velocity (RV)
dispersion of nine of twelve known young bona fide and candidate brown dwarfs
in the Cha I dark cloud is 2.0 km/s, i.e. significantly smaller than the RV
dispersion of T Tauri stars in Cha I (3.6 km/s) and only slightly larger than
the dispersion of the surrounding molecular gas (1.2 km/s) (Mizuno et al.
1999). This result indicates that the majority of these brown dwarfs are not
ejected with high velocity out of a dense region as proposed by some formation
scenarios for brown dwarfs. The mean RV values are consistent with the objects
being kinematic members of Cha I. The RV dispersion of the T Tauri stars
confined to the Cha I region is based on a compilation of T Tauri stars with
known RVs from the literature plus three T Tauri stars observed with UVES and
unpublished RVs for nine T Tauri stars. Time-resolved spectroscopy revealed RV
variations for five out of nine of the bona fide and candidate brown dwarfs in
Cha I, which could be due to orbiting planets or surface features. Furthermore
we derived rotational velocities vsin(i) and the Lithium 6708 \AA equivalent
width.Comment: A&A Letter, in pres
Congenital bronchial atresia: a fortuitous diagnosis.
A 25-year-old woman is admitted in the Radiology Department to evaluate by echography a tumefaction in the right axillary region. Multiple lymph nodes are found and the examination is completed by neck computed tomography. The presence of inflammatory lymph nodes associated with a positive serology for Bartonella Henselae led to the diagnosis of «Cat-scratch disease». Fortuitously, we discovered a hypodense left upper lung. A chest CT in breathing in and out revealed bronchial discontinuity of the apicoposterior left upper lobe bronchus. Associated radiological signs were: air trapping in the culmen while breathing out (Fig. A), local hypovascularization, small bronchoceles (Fig. B, arrow) and the presence of two bronchogenic cysts in the upper (Fig. C) and lower mediastinum
Preferred sunspot longitudes: Non-axisymmetry and differential rotation
As recently found, the distribution of sunspots is non-axisymmetric and spot
group formation implies the existence of two persistent active longitudes
separated by 180 degrees. Here we quantitatively study the non-axisymmetry of
sunspot occurrence. In a dynamic reference frame inferred from the differential
rotation law, the raw sunspot data show a clear clustering around the
persistent active longitudes. The differential rotation describing the dynamic
frame is quantified in terms of the equatorial angular velocity and the
differential rotation rate, which appear to be significantly different from
those for individual sunspots. This implies that the active longitudes are not
linked to the depth of sunspot anchoring. In order to quantify the observed
effect, we introduce a measure of the non-axisymmetry of the sunspot
distribution. The non-axisymmetric component is found to be highly significant,
and the ratio of its strength to that of the axisymmetric one is roughly 1:10.
This provides additional constraints for solar dynamo models.Comment: 7 pages, 8 figures, Astronomy and Astrophysics, in pres
The effect of starspots on eclipse timings of binary stars
We investigate the effects that starspots have on the light curves of
eclipsing binaries and in particular how they may affect the accurate
measurement of eclipse timings. Concentrating on systems containing a low-mass
main-sequence star and a white dwarf, we find that if starspots exhibit the
Wilson depression they can alter the times of primary eclipse ingress and
egress by several seconds for typical binary parameters and starspot
depressions. In addition, we find that the effect on the eclipse ingress/egress
times becomes more profound for lower orbital inclinations. We show how it is
possible, in principle, to determine estimates of both the binary inclination
and depth of the Wilson depression from light curve analysis
The effect of depressed starspots on the O-C diagrams of eclipsing systems is
also investigated. It is found that the presence of starspots will introduce a
`jitter' in the O-C residuals and can cause spurious orbital period changes to
be observed. Despite this, we show that the period can still be accurately
determined even for heavily spotted systems.Comment: 7 pages, 9 figures, accepted for publication in MNRA
Features of spatial distribution of oscillations in faculae regions
We found that oscillations of LOS velocity in H-alpha are different for
various parts of faculae regions. Power spectra show that the contribution of
low-frequency modes (1.2 - 2 mHz) increase at the network boundaries. Three and
five- minute periods dominate inside cells. The spectra of photosphere and
chromosphere LOS velocity oscillations differ for most faculae. On the other
hand, we detected several cases where propagating oscillations in faculae were
manifest with a five-minute period. Their initiation point on spatial-temporal
diagrams coincided with the local maximum of the longitudinal magnetic field.Comment: 6 pages, 4 figure
Spectral Inversion of Multi-Line Full-Disk Observations of Quiet Sun Magnetic Fields
Spectral inversion codes are powerful tools to analyze spectropolarimetric
observations, and they provide important diagnostics of solar magnetic fields.
Inversion codes differ by numerical procedures, approximations of the
atmospheric model, and description of radiative transfer. Stokes Inversion
based on Response functions (SIR) is an implementation widely used by the solar
physics community. It allows to work with different atmospheric components,
where gradients of different physical parameters are possible, e.g., magnetic
field strength and velocities. The spectropolarimetric full-disk observations
were carried out with the Stokesmeter of the Solar Telescope for Operative
Predictions (STOP) at the Sayan Observatory on 3 February 2009, when neither an
active region nor any other extended flux concentration was present on the Sun.
In this study of quiet Sun magnetic fields, we apply the SIR code
simultaneously to 15 spectral lines. A tendency is found that weaker magnetic
field strengths occur closer to the limb. We explain this finding by the fact
that close to the limb, we are more sensitive to higher altitudes in an
expanding flux tube, where the field strength should be smaller since the
magnetic flux is conserved with height. Typically, the inversions deliver two
populations of magnetic elements: (1) high magnetic field strengths (1500-2000
G) and high temperatures (5500-6500 K) and (2) weak magnetic fields (50-150 G)
and low temperatures (5000-5300 K).Comment: 10 pages, 6 figures, accepted for Solar Physic
The GREGOR Fabry-P\'erot Interferometer
The GREGOR Fabry-P\'erot Interferometer (GFPI) is one of three first-light
instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio
del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated
mounting. Thanks to its large-format, high-cadence CCD detectors with
sophisticated computer hard- and software it is capable of scanning spectral
lines with a cadence that is sufficient to capture the dynamic evolution of the
solar atmosphere. The field-of-view (FOV) of 50" x 38" is well suited for quiet
Sun and sunspot observations. However, in the vector spectropolarimetric mode
the FOV reduces to 25" x 38". The spectral coverage in the spectroscopic mode
extends from 530-860 nm with a theoretical spectral resolution R of about
250,000, whereas in the vector spectropolarimetric mode the wavelength range is
at present limited to 580-660 nm. The combination of fast narrow-band imaging
and post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales down to
about 50 km on the solar surface.Comment: 14 pages, 17 figures, 4 tables; pre-print of AN 333, p.880-893, 2012
(AN special issue to GREGOR
Large-scale horizontal flows in the solar photosphere II: Long-term behaviour and magnetic activity response
Recently, we have developed a method useful for mapping large-scale
horizontal velocity fields in the solar photosphere. The method was developed,
tuned and calibrated using the synthetic data. Now, we applied the method to
the series of Michelson Doppler Imager (MDI) dopplergrams covering almost one
solar cycle in order to get the information about the long-term behaviour of
surface flows. We have found that our method clearly reproduces the widely
accepted properties of mean flow field components, such as torsional
oscillations and a pattern of meridional circulation. We also performed a
periodic analysis, however due to the data series length and large gaps we did
not detect any significant periods. The relation between the magnetic activity
influencing the mean zonal motion is studied. We found an evidence that the
emergence of compact magnetic regions locally accelerates the rotation of
supergranular pattern in their vicinity and that the presence of magnetic
fields generally decelerates the rotation in the equatorial region. Our results
show that active regions in the equatorial region emerge exhibiting a constant
velocity (faster by 60 +/- 9 m/s than Carrington rate) suggesting that they
emerge from the base of the surface radial shear at 0.95 R_sun, disconnect from
their magnetic roots, and slow down during their evolution.Comment: 9 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
Observational study of chromospheric heating by acoustic waves
Aims. To investigate the role of acoustic and magneto-acoustic waves in
heating the solar chromosphere, observations in strong chromospheric lines are
analyzed by comparing the deposited acoustic-energy flux with the total
integrated radiative losses.
Methods. Quiet-Sun and weak-plage regions were observed in the Ca II 854.2 nm
and H-alpha lines with the Fast Imaging Solar Spectrograph (FISS) at the 1.6-m
Goode Solar Telescope (GST) on 2019 October 3 and in the H-alpha and H-beta
lines with the echelle spectrograph attached to the Vacuum Tower Telescope
(VTT) on 2018 December 11 and 2019 June 6. The deposited acoustic energy flux
at frequencies up to 20 mHz was derived from Doppler velocities observed in
line centers and wings. Radiative losses were computed by means of a set of
scaled non-LTE 1D hydrostatic semi-empirical models obtained by fitting
synthetic to observed line profiles.
Results. In the middle chromosphere (h = 1000-1400 km), the radiative losses
can be fully balanced by the deposited acoustic energy flux in a quiet-Sun
region. In the upper chromosphere (h > 1400 km), the deposited acoustic flux is
small compared to the radiative losses in quiet as well as in plage regions.
The crucial parameter determining the amount of deposited acoustic flux is the
gas density at a given height.
Conclusions. The acoustic energy flux is efficiently deposited in the middle
chromosphere, where the density of gas is sufficiently high. About 90% of the
available acoustic energy flux in the quiet-Sun region is deposited in these
layers, and thus it is a major contributor to the radiative losses of the
middle chromosphere. In the upper chromosphere, the deposited acoustic flux is
too low, so that other heating mechanisms have to act to balance the radiative
cooling.Comment: 11 pages, 10 figures, 3 table
Recommended from our members
Observational study of chromospheric heating by acoustic waves
Aims. Our aim is to investigate the role of acoustic and magneto-acoustic waves in heating the solar chromosphere. Observations in
strong chromospheric lines are analyzed by comparing the deposited acoustic-energy flux with the total integrated radiative losses.
Methods. Quiet-Sun and weak-plage regions were observed in the Ca ii 854.2 nm and H lines with the Fast Imaging Solar Spectrograph
(FISS) at the 1.6-m Goode Solar Telescope on 2019 October 3 and in the H and H lines with the echelle spectrograph
attached to the Vacuum Tower Telescope on 2018 December 11 and 2019 June 6. The deposited acoustic energy flux at frequencies
up to 20 mHz was derived from Doppler velocities observed in line centers and wings. Radiative losses were computed by means of
a set of scaled non-local thermodynamic equilibrium 1D hydrostatic semi-empirical models obtained by fitting synthetic to observed
line profiles.
Results. In the middle chromosphere (h = 1000â1400 km), the radiative losses can be fully balanced by the deposited acoustic energy
flux in a quiet-Sun region. In the upper chromosphere (h > 1400 km), the deposited acoustic flux is small compared to the radiative
losses in quiet as well as in plage regions. The crucial parameter determining the amount of deposited acoustic flux is the gas density
at a given height.
Conclusions. The acoustic energy flux is e ciently deposited in the middle chromosphere, where the density of gas is su ciently
high. About 90% of the available acoustic energy flux in the quiet-Sun region is deposited in these layers, and thus it is a major
contributor to the radiative losses of the middle chromosphere. In the upper chromosphere, the deposited acoustic flux is too low, so
that other heating mechanisms have to act to balance the radiative cooling
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